The present invention relates, in general, to image processing and, more particularly, to interlaced video signals.
In the broadcast television industry, video signals are transmitted from a transmitter to a receiver as interlaced video signals. Typically, the receiver is a television set or television monitor. In the television set, a picture tube generates light by sending a beam of electrons to a phosphor coated screen or face. The phosphors emit visible light when hit by the electrons. The intensity of the light does not remain constant but decays with time. The amount of time that the light remains visible is called persistence. Typically, designers design the picture tubes such that the light decays at a rate that allows movement on a television screen without leaving artifacts behind, e.g., if the persistence is too long, movement will smear the image. Thus, the designer tailors the decay of the light, i.e., the properties of the phosphors, as a compromise between flicker and the smearing of movement.
Interlaced video signals make use of two sweeps of the picture tube to present a single image. Each sweep is called a field and two fields together comprise a frame. Each field starts at the top left of the screen and every other horizontal line is drawn from left to right moving down the screen. Thus the lines above and below every line in a frame come from an opposite field. Fields are also referred to as being even and odd or first and second. Although this technique halves the required bandwidth, it results in flicker.
More particularly, flicker occurs if a single horizontal line in one field has a brightness significantly more intense than the lines that are above and below it in the opposing field. The flicker results from the bright line decaying without its brightness being replaced by the lines from the opposing field. Because the light decays at approximately one-thirtieth of a second, it is perceptible to the human eye. This is irritating to the person watching the television screen.
Hence, a need exists for a method and an apparatus to reduce flicker. It would be advantageous for this method and apparatus to be low cost and easy to implement.